Comparison of semi‐empirical and density functional approaches for the colour and constitution of anthraquinone dyes using X‐ray structure

Abstract

Theoretical calculations with density functional theory, semi-empirical PM5 random phase approximation and Zerner's intermediate neglect of differential overlap CI were carried out for various amino and hydroxy anthraquinones using X-ray structure data. Comparing quantum chemical calculation results based on X-ray structure, the PM5 random phase approximation method was the most promising for the prediction of λ max for anthraquinone dyes among the computational methods studied here. From the results of calculated gross population, p z , it was found that the value of p z using the time-dependent density functional theory method was greater than the values calculated by semi-empirical methods. The overestimation of p z could be attributed to the incorrect density functional theory calculation results. The results of PM5 random phase approximation-calculated oscillator strength and torsion angle showed reasonable agreement with the observed results for sterically hindered anthraquinone dyes.